Real-time models of morphogenetic processes.

Morphological transformations are often describable by simple series kinetic models, A----B, A----B----C, etc., which allow assessment of the rates of interconversion of the distinguishable shapes or forms present and their probabilities of occurrence at various points in time, thus providing a means for kinetic comparisons with biochemical measurements of the molecular-level reactions that cause the transformations. When changes in cell morphology are followed turbidimetrically, the real-time progress curves can be simulated by fitting the data to a form of Beer's law for scattering by mixtures in which the species concentrations change with time in accordance with the chosen kinetic scheme. Because many even relatively large cells are mostly water, classical light scattering theory can be used to interpret the turbidimetric data in terms of simple geometrical models of average cell size and shape suggested by microscopic examination. Two examples are briefly considered, the stimulus-induced changes in blood platelet shape and apparent size and their correlation with cytosolic-free calcium, and apparent swimming motion exhibited by neutrophils in suspension.